Contact alloy and method of making same



.l atente'dJan. 7,1941

CONTACT ALLOY AlgTD METHOD OF G t i H. Briggs, Highland Park, and Childress B.

. Gwyn, In, Bannockburn, Ill., assignors to Fansteel Metallurgical Corporation, North Chicago,

a f7 Claims. This invention relates to electrical Provisionoi'an electrical make-and-break contact of novel composition and: of a novel method For so muchof the subject matter as is com- .mon, we claim the priority-of our application, Serial No. 13,300, filed April 8, 1936, of which this application is a continuation in part.

Prior to this invention the metal tungsten was considered 1 physical.- chemical and electrical properties by or desired in 'fltlctrical make-,and-break contacts. a

. No other metal'or alloy was known which even fairly approximated tungsten in these qualities.

Tungstennnetal has been worked and treated by variousgmethod's with a view to causing these desired properties to become more or less pronounced orjof changing the nature of the metal itself ,to secure optimum performance. Commercialtungsten contacts are; however, made by a method involving 'sin'tering pressed tungsten powder at arelaltively high temperature, working the in ot thus formed, as by swaging or rolling, and either cutting contact discs fromtungsten rods or-punching them from rolled tungsten sheet; Securing the necessary high sintering temperatures .inuolved con'siderable expense, and the cutting and pu ching operations result in a scrap loss which, taking into consideration the cost of production and material, is quite considerable. Up tothe time of our invention no process eliminating any'of these steps has to, our

knowledge been commercially successful.

3- Another object of the invention is to produce (an'electricalfmake-and-break contact with substantially the .same properties as commercial tungsten contacts by a heat treatment at a relativel'y low temperature. and by a method which l eliminates-or, at, least, minimizes scrap loss.

n further object of the invention isto provide a composite contact of. tungsten and nickel so intimately mixed therewith that noto'nly is the; sintering temnegaturegmaterially reduced below that of'ltungsten, but in addition the intermixed tungsten and nickel result in a contact which hasv practically the sameproperties as -a contact of tungsten withoult the nickel ,still another object of ou'rinvention is to produce analloy of tungsten and nickel difiering in a.

composition? and physical. character {from I previously-known alloys of these two metals;

: Other objects of the invention'will be'comeapparent from the roilowing description of an em- I make-andbreak contacts and hasfor a general object the for making electrical make-and-break. contacts.

as possessing the most nearly ideal 111., a corporation of New York bodiment exemplifying some of the features of the invention.

In order to accomplish the foregoing objects, we provide a sintered, composite, make-andbreak contact comprising tungsten as the principal contact material in an amount predominating by weight in the contact, and nickel, as the auxiliary contact material or binder in a significant but minor percentage by weight.

' The percentagesof-the tungsten and nickel are dependent somewhat upon the contact for which the resulting contact is intended. l

- On the one hand, the lower limit of the nickel is-'(l) that amount below which it has not been thought possible to sinter the mixture at a relatively low temperature of the order of, 1500 C.; (2) even though sintering is possiblewith, the percentage employed, the electrical properties of the finished product may not be desirable. The minimum' useful amount, depending on either one or the other of these two factors, is found T to be approximately' per cent.

On the other hand, the upper limit of the nickel is also necessarily a. minor percentage by weight, since otherwise, due to the relative'atomlc weights the volumetric proportions may be such, ,that thedesirable resistance to migration or 1 transferof contact material contributed by thetungsten may be lowered to an objectionable amount. Ordinarily an upper limit for the nickel should rarely exceed 4% by weight of the contact andshould never exceed 8 per cent by weight,

since greater percentages have not been found to contribute any desirable properties. to the contact. f

The nickel may thus be varied between the (limits just stated and the tungsten makes up the remainder of the novel electrical make-a'nd-break contact, and we have found that contacts of from about one per cent to about two per cent by weight .of nickel, the remainder being tungsten, are particularly suitable. for use in the ignition control circuits of certain automobiles, although suitable contacts'have been made with asllttle as one-half of one percent nickel.

' Briefly stated, the novel contact of the inventionmay be made by providing an intimate mixture of tungsten and nickelin the desired proportions, pressing the mixture into a pellet of the desired contact shape and substantially to the desired size allowing for shrinkage during the .ensuing heattreatment, and sintering the pellet.

Preferably the intimate mixture of the tungresulting product and which provides a mixture of tungsten and nickel ,in astate of what we call "atomic dispersion-since the mixture seems so thorough and uniform that apparently the individual atoms of the tungsten and nickel are dis-. tributed throughout, the mass in the same pro-.

portions as would obtain in a. definite chemical compound of the same formula. Such an initimate mixture is obtained byreducing or' other;

wise treating a compound containing suitable proportions of tungsten and nickel to remove the undesirable constituenxtsirom the compound and to convent it into. an intimate mixture of tungsten and nickel.

Ii contacts of disc shape are desired, dies are. employed with diameters which allow for shrinkage due to a sintering, so that the subsequent sintering of the pressed powders will result in contacts of the desired diameters. -'Ihe thickness of each disc is controlled by theweight of the powder supplied to each die for pressing and by the. pressure employed. The powder mixture of tungsten and nickel is thus pressed into pellets at a forming pressure, which permits handling the pressed pellets and those pellets. are heated in an-atmosphere of hydrogen or other neutral orreducing atmospheres or in a vacuum to a sintering temperature for about one-half hour, the sintering temperature being. in. theorder of 1500 contacts.

Illustrative. ofour novel method, as described above, we add a soluble ammonia compound of nickel to a-clear solutionof tungstic acid in ammonium hydroxide, the while constantly stirring the mixture. Onesuch soluble ammonia compound of nickel may be prepared from the chloride according to the formula Nick-(EH20. An amount of that chloride providing the desired weight equivalent of nickel may be dissolved in water, and ammonium hydroxide may then be added to that solution untilthe characteristic bluish-green precipitate, which is formed at first, is again dissolved. For example, for a contact .with 2 per cent of nickel, 25.3 grams of nickel chloride (NiCh) '6H2O (equivalent to 6.8 grams of metallic nickel) j are employed in preparing the soluble ammonia compound of nickel already described.

An amount of tungstic acid providing the de-.

sired weight. equivalent of tungsten, is dissolved in sufilcient ammonia to jform a clear solution known as. ammonium tungstate. for a contact with 98% of tungsten, 490, grams of tungstic acid are-dissolved in the ammonia.-

While constantly stirring that solution, as ;al-\

ready explained, the soluble ammonia compound of nickel described above is added thereto. If-the ammonia is in suflicient excess, no precipitate is obtained when the two solutions are thus mixed,

but as the mixture is heated to expel the *mmonia, a greenish precipitate of green nickel tungstate, NiWOr, and tungstic acid, is formed.

The heating of the mixture is continued until the precipitate is dry;

The dried precipitate just-described, is heated v to about 200 C to expel excess ammonium salts and the-precipitate is reduced by heating it in Lydrogem'in a well known manner, to yield a powder mixture of tungsten and nickel, with the propergrain or particle size for pressing into pellets and sintering as already described.

In carrying our our process we" deliberately neck to obtain an alloy which is substantially intermittently.

0., depending upon the relative amounts of tungsten and nickel employed in the For example,

non-ductile. this-procedure results in th production of an alloy which is relatively coarsegrained; that is to say," the grain size approximatesthat oi the commercial grades 10f tungsten now used fohcdntactpurp'osigsi This condition is brought about by ma'intainingjhe sintering time and temperature at suiiiciently high values to secure the desired grain growth. For example, weprefer to sinter a 1 per cent nickel alloy for 40 minutes at 1500 C; in-*hydrogen Another result of this method of procedure is tc bring about the-segregation of substantiallyall the nickel in the form of nickel-tungstemallo; at the grain boundaries. A typical. structure resulting from the-practice of our invention is illustrated at Fig. 3 of the drawings of an application. or the inventor, Briggs; herein,,-and ,William 'Lenz, Serial Number 256,207 filed February 13,1939; I

In order to test the contact performance of 0111 novel contact, a-pairof such contactswas employed ina-llO-volt A. C. lighting circuit ir which two -watt lamps in parallel were lighte'c The peak current amounted tn apprpximately Llamperes. At'the end of 12 hours, about 1,296,000 contacts having meanwhile been made and-broken by the pairof contacts, the contacts were removed and examined for. oxidation and-wear. Thesurfaces of the contacts were unusually clean and the contact surface wearof each contact was about 0.01(

inches, although the contact surface radius 01 the "test contacts was-unusually small, about 0.5 inch, and therefore unfavorable to such gooc results as were obtained in the test. 1 X

After 100 hours of operation under the tesi conditions just described, a pair of commercia contacts consistingof tungsten had a contact resistance-of 0.003 ohm as compared with the foilowing'po'tential drops of typical composit:

contacts having the indicated formulas anc tested underthesame conditions for the respective periods shown below: 1

, Thus, the electrical durability of our compo site contact compares favorably-with well know! commercialcontacts of tungsten.

Likewise, the physical'characteristics of on novel contact, as exemplified by .the smal amount of wear recited above, and as furthe:

' shown by the following hardness comparisons indicate the utility of the invention. The hard .ness orthe commerciahtungsteni contacts on th Rockwell A scale measured 66.. On the sam scale our contacts with 96% tunBsten;and 4% nickel *were hard: our contacts with 09 2 tungsten and nickel were 66 hard: our con tacts with 99% tungsten and 1% nickel were 6| hard; our contacts with 98% tungsten and 2a nickel were 06 hard.

While we have described 'agp'referred embodi ment of our invention, many modifications ma; be made without departing irom the spirit 0 the-invention, and we do not wish to be limited to the precise details or construction set forth. but desire to avail ourselves oi all changes vvitln in the scope of the appended claims.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent oi the United States, is:

1. Analloy-consisting essentially of from about 96 to 99% per cent by weight oi'tungsten, and

from about i to /2 per cent by weight 01 nickel, said alloy being characterized in .the unworked 'condition', .when sinteredaboye 1500- C. for

- nickel content segregated at the grain boundaries,

periods ot the order of one-'halt hour and more by being iorthe rnost part made up of large well grown crystals, with the major portion oi the said alloy being further characterized by substantially thenon-ductlle and electrical qualities of commerciallypure' tungsten contacts.

2. An alloy consisting essentially of from about 98 to 99 per cent by weight of tungsten, and iromabout 2 to 1 per cent by weight or nickel, said al'-.

. loy being characterized in the unworked condipart made up of large well grown' crystals, with 1 'thamaior portion 0! the nickel content segre- .40

tion, when sintered above 1500 C. for periods of the order of one-half hour and more by'beingfor the most part made up 0! ,la'rgewell grown crystals, with the major, portion of the nickel content segregated at the grainrboundaries, said alloy being iurthercharacterized by substantially the nondu'ctile-and electrical qualities of commercially puretungsten contacts. Q

of one-halt hour and more by being for the most part made up of large well grown crystals, with the major portion of the nickel content segre gated at the grain boundaries, said alloy being further characterized by substantially the nonductile' and electrical qualities'oi commercially pure tungsten contacts.

5. An electrical make-and-b'reak contact comprising an unworked, sintered-to-shape body consisting essentially of an alloy of from about 98 to 99 per cent by weight of tungsten and from about 2 to-l per cent by weight or nickel, said alloy for the most part made up 0! large, well-grown crystals, produced by sintering above 1500 C. for a j period of the order oi one-halt hour and longer the major portion of the nickel content being segregated-1 at the grain boundaries, said alloy being further characterized by substantially the nonductile and electrical qualities of commercially ,pure tungsten.

6. An electrical make-and-break contact comprising an unworked, sinterecl-to-shape body consisting essentially of an alloy of about 99 per cent by weight of tungsten and about 1 per cent 3. Anallo'y consisting essentially of about 99 per cent by weight oi tungsten, and about 1 per cent by weight or nickel, said alloy being characterized in the unworked condition, when sintered above -.150(i C, for periodsbf the order of one-half hour and more by being .ior the most gated at the grain boundaries, said alloy being furthertcharacterized by substantially the nonductile and electrical qualities of commercially pure. tungstencontacts. r

4. An alley consisting oi essentially of about 99%per cent by weight of tungsten and about V2 per cent by weight oi nickel saidalloy being characterized in the unworked condition, when sinter'ed above 1500 C. for periods of the order "applications, which comprises obtaining tungsten metalpower admixed with from. about A; to 4. percent by weight of nickel, pressing from the mixture a body of the desired shape and of suiflciently larger size to allow for subsequent 1 shrinkage, and sintering the body at 1506" C. and

upwards in a non-oxidizing atmosphere for sufflcient time of the order of half anhour and upwards to produce the desired dense body having relatively large, well-grown grains.

' FRANK H. BRIGGS.

CHILDRESS B. GWYN, JR.

CERTIF ICA'I'E OF 'CORREQTION. I v

u iI-V, 19

' RANK HQ DRIGGS, ET AL; v It is'hefebf' cgfiified that error alppears in the printed spe c1 f 1 m aiadvqhmnbered patgnt rgquiring correcztlor a.- as follqws: Pa ge colfimn', 15,368 .8 and 9 s tri-ke but the cpnima and words of W1.

pat t N ,2 7,4 5

applicatiori is'a' cpntiim'a'tion in part" isampagez-seiond column) zifbeaz- "gzorltacif"insertF ags-1 page 2, f1rstcolumn, line 17,-befc taxin str ike out 1 11b artile ""a" ;'.11ne 5' o', for "1 00. 0," read --1 c 1m; Tit, for "oin" our" red --putour--; and that th bald Lettp z I "should 5e ead 'wuh this correction therein that me same may c" thediacord df'fihe base in the Patent office.

fsi'gned' and sealed thia l'jth day df April, A; '9'; 19m.

I Ienry Van'AI-sda (Seal) Ac t ing Qommissloner o1 CEHIIFICATEOF CORRECTION. 1 Patent No. 2,227,415. J n Sr'Y, 9b

' FRANK E. DRIGGS, ET AL. t It is hereby" certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Pagel, first col'bmn lines 8 and 9, strike out the comma and words of which this application is-a continuation in part"; same page second column line ll, after 'c'ontact" insert i1se-Y-; page 2, first column, line 17, before "sintering" mi e out the article "a"; line 0, for "1 00 0." read --1 oo c.--; line 714:, for "our our read -out our--; and that the said Letters Patent should he read with this correction therein that the same may conform to jthe 'record' of'the case in the Patent Office.

-Si'gned' and sealed this 15th day, of April, A". D; 1941.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

